Diffusing gas turbine engine recuperator

ABSTRACT

A method of diffusing and cooling an exhaust flow in an exhaust duct of a gas turbine engine includes circulating the exhaust flow from a turbine section of the gas turbine engine to a recuperator extending within the exhaust duct, circulating air discharged from a compressor section to a combustor of the gas turbine engine through air passages of the recuperator, and cooling and diffusing the exhaust flow by circulating the exhaust flow through exhaust passages of the recuperator having a progressively increasing cross-sectional area and in heat exchange relationship with the air passages.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 13/036,428filed Feb. 28, 2011, the entire contents of which are incorporated byreference herein.

TECHNICAL FIELD

The application relates generally to a recuperator for a gas turbineengine and, more particularly, to such a recuperator allowing for adiffusion of the exhaust flow circulating therethrough.

BACKGROUND OF THE ART

Gas turbine engines may include a recuperator, which is a heat exchangerusing hot exhaust gas from the engine to heat the compressed air exitingthe compressor prior to circulation of the compressed air to thecombustion chamber. Preheating the compressed air usually improves fuelefficiency of the engine. In addition, the recuperator reduces the heatof exhaust gas, which helps minimize the infrared signature of theaircraft.

SUMMARY

In one aspect, there is provided a recuperator configured to extendwithin an exhaust duct of a gas turbine engine, the recuperatorcomprising exhaust passages providing fluid flow communication betweenan exhaust inlet and an exhaust outlet, the exhaust inlet being orientedto receive exhaust flow from a turbine of the engine and the exhaustoutlet being oriented to deliver the exhaust flow to atmosphere, theexhaust inlet having a smaller cross-sectional area than that of theexhaust outlet, and a cross sectional area of each exhaust passageprogressively increasing from the exhaust inlet to the exhaust outletsuch as to diffuse the exhaust flow, air passages in heat exchangerelationship with the exhaust passages and providing fluid flowcommunication between an air inlet and an air outlet, an inletconnection member defining the air inlet and being designed to sealinglyengage a first plenum in fluid flow communication with a compressordischarge of the gas turbine engine, and an outlet connection memberdefining the air outlet and being designed to sealingly engage a secondplenum containing a compressor of the gas turbine engine.

In another aspect, there is provided a gas turbine engine comprising acompressor section having a discharge in fluid flow communication with afirst plenum, a combustor contained in a second plenum, a turbinesection in fluid flow communication with the combustor, an exhaust ductin fluid flow communication with the turbine section, and a recuperatorlocated in the exhaust duct, the recuperator defining: exhaust passagesproviding fluid flow communication between an exhaust inlet and anexhaust outlet, the exhaust inlet and exhaust outlet extending acrossthe exhaust duct with the exhaust inlet being in fluid flowcommunication with the turbine section, the exhaust inlet having asmaller cross-sectional area than that of the exhaust outlet, and across sectional area of each exhaust passage progressively increasingfrom the exhaust inlet to the exhaust outlet such as to diffuse theexhaust flow, air passages in heat exchange relationship with theexhaust passages and providing fluid flow communication between an airinlet and an air outlet, an inlet connection member defining the airinlet and sealingly engaging the first plenum to receive pressurized airfrom the compressor, and an outlet connection member defining the airoutlet and sealingly engaging the second plenum containing thecombustor.

In a further aspect, there is provided a method of diffusing and coolingan exhaust flow in an exhaust duct of a gas turbine engine, comprisingcirculating the exhaust flow from a turbine section of the gas turbineengine to a recuperator extending within the exhaust duct, circulatingair discharged from a compressor section to a combustor of the gasturbine engine through air passages of the recuperator, and cooling anddiffusing the exhaust flow by circulating the exhaust flow throughexhaust passages of the recuperator having a progressively increasingcross-sectional area and in heat exchange relationship with the airpassages.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2 is a partial cross-sectional view of a gas turbine engine,showing a recuperator according to a particular embodiment;

FIG. 3 is a schematic tridimensional view of a gas turbine engineincluding the recuperator of FIG. 2, with one segment thereof removed;

FIG. 4 is a tridimensional view of the recuperator of FIG. 2, with onesegment thereof omitted;

FIG. 5 is a tridimensional view of a segment of the recuperator of FIG.2;

FIG. 6 is an exploded tridimensional view of the segment of FIG. 5;

FIG. 7 is a partial cross-sectional view of a gas turbine engine,showing the recuperator of FIG. 2 with a diffuser attached thereto;

FIG. 8 is a partial cross-sectional view of a gas turbine engine,showing a recuperator according to another embodiment;

FIG. 9 is a tridimensional view of the recuperator of FIG. 8;

FIG. 10 is a tridimensional view of a segment of the recuperator of FIG.8, with a side plate removed;

FIG. 11 is a schematic cross-sectional view of a floating connectionbetween the recuperator of FIG. 8 and a plenum of the gas turbineengine;

FIG. 12A is a schematic representation of the shape of cold air cells ofthe recuperator of FIG. 8; and

FIG. 12B is a schematic representation of the shape of the cold aircells of taken along direction B of FIG. 12A.

DETAILED DESCRIPTION

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight, generally comprising in serial flowcommunication a fan 12 through which ambient air is propelled, acompressor section 14 for pressurizing the air, a combustor 16 in whichthe compressed air is mixed with fuel and ignited for generating anannular stream of hot combustion gases, and a turbine section 18 forextracting energy from the combustion gases. The compressor section 14and combustor 16 are typically in serial flow communication with oneanother through a gas generator case 22 which contains the combustor 16and which receives the flow from the compressor discharge, which in theembodiment shown is in the form of diffuser pipes 20. The combustiongases flowing out of the combustor 16 circulate through the turbinesection 18 and are then expelled through an exhaust duct 24.

Although illustrated as a turbofan engine, the gas turbine engine 10 mayalternately be another type of engine, for example a turboshaft engine,also generally comprising in serial flow communication a compressorsection, a combustor, and a turbine section, and a propeller shaftsupporting a propeller and rotated by a low pressure portion of theturbine section through a reduction gearbox.

Referring to FIG. 2, in the present embodiment, the gas generator case22 is separated in at least two plenums, including a plenum 26containing the combustor 16, and another plenum 28 in fluid flowcommunication with the diffuser pipes 20 of the compressor section 14.

A recuperator 30 extends across the exhaust duct 24, such that theexhaust gas from the turbine section 18 circulates therethrough. Therecuperator 30 also provides the fluid flow communication between thecombustor plenum 26 and the compressor plenum 28, as will be furtherdetailed below.

Referring to FIG. 3-6, the recuperator 30 includes a plurality ofarcuate segments 32, which function independently from one another andare connected to the engine 10 independently from one another, and whichtogether define the annular shape of the recuperator 30. A controlledgap 34 (see FIG. 4) is provided between adjacent ones of the segments 32to allow for thermal expansion without interference. In a particularembodiment, the segments 32 are sized to extend between adjacentstructural struts 36 (see FIG. 3) of the engine 10, and as such the gap34 is sized to allow for thermal expansion of each segment 32 withoutmajor interference with the strut 36 extending in the gap 34. Acompressible side plate 46 at the side of the segment 32 providessealing with the strut 36 and vibrational damping during engineoperation. In the embodiment shown, each segment 32 is sized and locatedsuch as to be removable from the outside of the engine 10 through anopening accessible when the exhaust scroll 38 (see FIG. 2) is removed.With an exhaust scroll 38 that is removable on the wing, such aconfiguration allows for the recuperator segments 32 to be removed andreplaced if necessary with the engine 10 remaining on the wing.

Referring particularly to FIGS. 5-6, each segment 32 defines a plateheat exchanger, with a first group of fluid passages 40 for circulatingthe compressed air, and a second group of fluid passages 42 forcirculating the exhaust gas. The air and exhaust passages 40, 42alternate and are in heat transfer relationship with one another. In theembodiment shown, the air and exhaust passages 40, 42 are relativelyoriented such as to define a mixed counter flow and double pass crossflow heat exchanger. A panel assembly 44 thus defines the alternatingU-shaped first fluid passages 40 and curved second fluid passages 42. Ina particular embodiment, the panels 44 are made of a nickel alloy andare brazed to one another. The side plates 46 and a rear bulkhead 48respectively seal the opposed side ends and the rear end of the panelassembly 44. The bulkhead 48 also provides vibrational damping of thesegment 32 during engine operation.

The exhaust fluid passages 42 communicate with a same exhaust inlet 50defined by the radially inward end of the segment 32 and with a sameexhaust outlet 52 defined by the radially outward end of the segment 32.The exhaust inlet and outlet 50, 52 extend across the exhaust duct 24,with the exhaust inlet 50 located in proximity of the turbine section18.

Referring to FIGS. 5-6, the air passages 40 communicate with a same airinlet 56 defined at one end thereof and with a same air outlet 72defined at the opposed end thereof. The air inlet 56 is defined by aninlet connection member 58 which is designed to sealingly engage thecompressor plenum 28 for receiving the compressed air. The air inlet 56is oriented such that the compressed air flows axially or approximatelyaxially therethrough. The inlet connection member 58 includes a duct 60having one end connected to an inlet bulkhead 62 attached to the panelassembly 44, and an opposed end having a flange 64 extending outwardlytherearound. Referring to FIG. 2, the inlet connection member 58 alsoincludes a flexible duct member 66 having a first end rigidly connectedto the flange 64, for example through an appropriate type of fastenerswith a compressible seal ring or a gasket (not shown) therebetween. Asecond end of the flexible duct member 66 is rigidly connected to thecompressor plenum 28. In the embodiment shown, the flexible duct member66 includes two rigid duct portions 68 interconnected by a diaphragm 70,which allows relative movement between the two duct portions 68;alternately, the entire flexible duct member 66 may be made of flexiblematerial. Accordingly, “flexible duct member” is intended herein todesignate a duct member which includes at least a flexible portion suchas to allow for relative movement between its opposed ends. The inletconnection member 58 thus defines a floating connection with thecompressor plenum 28, such that some amount of axial and radial relativemotion is allowed therebetween.

Referring back to FIGS. 5-6, the air outlet 72 is defined by an outletconnection member 74 which is designed to sealingly engage the combustorplenum 26 for delivering the heated compressed air to the combustor 16.The air outlet 72 is oriented such that the heated compressed air flowsaxially or approximately axially therethrough. The outlet connectionmember 74 includes a duct 76 having one end connected to an outletbulkhead 78 attached to the panel assembly 44, and an opposed end havinga flange 80 extending outwardly therearound. Referring to FIG. 2, theflange 80 is rigidly connected to the combustor plenum 26, for examplethrough an appropriate type of fasteners. A compressible seal ring or agasket (not shown) is received between the flanged 80 and the plenum 26to form a sealed connection. The outlet connection member 74 thusdefines a rigid connection with the combustor plenum 26.

Alternately, the inlet connection member 58 may define a rigidconnection with the compressor plenum 28, with the outlet connectionmember 74 defining a floating connection with the combustor plenum 26.

Referring back to FIG. 2, in the embodiment shown, the rear bulkhead 48includes a protrusion 82 which is designed to be the contact pointbetween the segment 32 and the wall 84 of the exhaust duct 24, in orderto stabilize the position of the segment 32 within the exhaust duct 24.The protrusion 82 facilitates the relative sliding motion between therear bulkhead 48 and the exhaust duct wall 84 when relative movement dueto the floating connection occurs, and acts as a control surfacemaintaining contact between the segment 32 and the exhaust duct wall 84.

In a particular embodiment, the exhaust passages 42 including theircurved portion have a flaring shape, i.e. the cross-sectional area ofeach exhaust passage 42 increases in the flow direction, from theexhaust inlet 50 to the exhaust outlet 52, such as to diffuse theexhaust flow. The exhaust inlet 50 thus has a smaller cross-sectionalarea than that of the exhaust outlet 52. Referring particularly to FIG.2, a concentric split diffuser 53 is provided in the exhaust duct 24upstream of the exhaust inlet 50. The diffuser 53 includescircumferential splitters 54 which are supported by radial struts 55.The splitters 54 progressively curve from the axial direction at theupstream end toward the radial direction. The splitters 54 definepassages having a flaring shape, i.e. with an upstream end having asmaller cross-sectional area than the downstream end, to diffuse of theexhaust flow further diffused within the recuperator 30. Diffuser vanes51 may also be provided at the exit of the power turbine, upstream ofthe split diffuser 53. The diffusion of the exhaust flow allows for animproved heat exchange within the recuperator 30.

In the alternate embodiment shown in FIG. 7, the concentric splitdiffuser 53′ including splitters 53′ and radial struts 55′ forms part ofthe recuperator 30, and extends from the exhaust inlet 50.

In a particular embodiment, the recuperator 30 also reduces the swirl ofthe exhaust flow. As can be seen from FIG. 4, the exhaust passages 42have an arcuate profile in a plane perpendicular to a central axis C ofthe recuperator to reduce the exhaust flow swirl. The splitters 54 (FIG.2) may also be curved in the plane perpendicular to the central axis ofthe recuperator. The radial struts 55, 55′ which are structural memberssupporting the splitters 54, 54′ (FIGS. 2 and 7) have an asymmetricalairfoil shape twisted to allow a progressively increased swirl withincreasing radius, optimised to reduce the turning losses as the flowturns from the axial to the radial direction within the diffuser 53,53′. The vanes 51 may also have an asymmetrical airfoil shape similar tothe struts 55, 55′. The swirl, i.e. the circumferential component of theflow velocity at the power turbine exit, is thus first slowed in thediffuser vanes 51. The flow exiting the vanes 51 enter the splitdiffuser 53, 53′. The flow in the split diffuser 53, 53′ slows down bothin the axial direction due to the splitters 54, 54′ as well as incircumferential direction, i.e. the swirl, due to the increased radiusof the swirling shape of the radial struts 55, 55′.

Referring now to FIGS. 8-12, a recuperator 130 according to an alternateembodiment is shown. The recuperator 130 includes a plurality ofindependent arcuate segments 132, with a controlled gap 134 beingdefined between adjacent segments 132 for thermal expansion. Eachsegment 132 defines a plate heat exchanger, with a first group of fluidpassages 140 for circulating the compressed air, and a second group 142of fluid passages for circulating the exhaust gas, alternating and inheat transfer relationship with one another.

The recuperator 130 extends within the exhaust duct 24 closer to theturbine section 18 than the previously described embodiment. Eachsegment 132 includes an exhaust inlet 150 defined by a radiallyextending end of the segment 132 located in proximity of the turbinesection 18 and in communication with the exhaust passages 142. Theexhaust inlet 150 is oriented such that the exhaust gas flows axially orapproximately axially therethrough. Each segment 132 also includes anexhaust outlet 152 in communication with exhaust passages 142, andoriented such that the exhaust gas flows outwardly radially orapproximately outwardly radially therethrough.

The air passages 140 communicate with a same air inlet 156 defined atone end thereof and with a same air outlet 172 defined at the opposedend thereof. The air inlet 156 is defined by an inlet connection member158 which is designed to sealingly engage the compressor plenum 28 forcirculating the compressed air. The air inlet 156 is oriented such thatthe compressed air flows axially or approximately axially therethrough.The inlet connection member 158 includes a support 164 surrounding theinlet 156 which is rigidly connected to the compressor plenum 28, forexample through an appropriate type of fasteners with a compressibleseal ring or a gasket (not shown) therebetween. The inlet connectionmember 158 thus defines a rigid connection with the compressor plenum28.

The air outlet 172 is defined by an outlet connection member 174 whichis designed to sealingly engage the combustor plenum 26 for deliveringthe heated compressed air to the combustor 16. The air outlet 172 isoriented such that the heated compressed air flows radially outwardly orapproximately radially outwardly therethrough. The outlet connectionmember 174 includes a duct 176 which is engaged in a correspondingopening of the combustor plenum 26. Referring to FIG. 11, a flexible andcompressible circular seal 94, for example having a C-shapedcross-section, surrounds the duct 176 and abuts the wall 98 of theplenum 26 around the opening where the duct 176 is received. A collar92, sandwiched between retaining rings 90, is received between the seal94 and an outwardly extending flange 96 of the duct 176, and compressesthe seal 94. The connection member 174 thus defines a floatingconnection with the combustor plenum 26, as some amount of axial andtangential relative motion is allowed between the connection member 174and the support opening of the plenum 26 to compensate for thermalmismatch. The circular seal 94 seals the connection.

As can be seen in FIG. 8 and FIG. 12B, the exhaust passages 142 definedbetween the air cells 141 forming the air passages 140, including thecurved portion of each exhaust passage 142, have a flaring shape such asto diffuse the exhaust flow. The exhaust inlet 150 thus has a smallercross-sectional area than that of the exhaust outlet 152. The diffusionof the exhaust flow allows for an improved heat exchange within therecuperator 130. In the embodiment shown, the recuperator 130 has ashape substantially confirming to that of the exhaust duct 24, with acontrolled gap 134 (see FIG. 11) being provided between the recuperator130 and exhaust duct wall to prevent restriction of the relativemovement allowed by the floating connection.

In a particular embodiment, the recuperator 130 also reduces the swirlof the exhaust flow. As can be seen from FIGS. 9 and 12B, the air cells141 forming the exhaust passages 142 act as vanes, and have an arcuateprofile in a plane perpendicular to a central axis C of the recuperatorto reduce the exhaust flow swirl. The air cells 141 thus define adiffusion area 99 and a deswirling and diffusion area 100, which act toslow down the exhaust flow both in the axial direction as well as incircumferential direction.

In the above described embodiments, each segment 32, 132 of therecuperator 30, 130 is only connected to the engine 10 through the inletand outlet connection members 58, 158, 74, 174, and the segments 32, 132are independent from each other. Since one of these connection membersdefines a floating connection, some relative movement is allowed betweeneach segment 32, 132 of the recuperator 30, 130 and the remainder of thegas turbine engine 10, such as to accommodate some amount of thermalexpansion without impeding the seal of the connections.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.Modifications which fall within the scope of the present invention willbe apparent to those skilled in the art, in light of a review of thisdisclosure, and such modifications are intended to fall within theappended claims.

1. A method of diffusing and cooling an exhaust flow in an exhaust ductof a gas turbine engine, comprising: circulating the exhaust flow from aturbine section of the gas turbine engine to a recuperator extendingwithin the exhaust duct; circulating air discharged from a compressorsection to a combustor of the gas turbine engine through air passages ofthe recuperator; and cooling and diffusing the exhaust flow bycirculating the exhaust flow through exhaust passages of the recuperatorhaving a progressively increasing cross-sectional area and in heatexchange relationship with the air passages.
 2. The method as defined inclaim 1, wherein circulating the exhaust flow from the turbine sectionto the recuperator includes circulating the exhaust flow throughpassages having a progressively increasing cross-sectional area anddefined by circumferential splitters of a diffuser located in theexhaust duct.
 3. The method as defined in claim 2, wherein the exhaustflow circulates through the passages defined by the circumferentialsplitters along a path oriented progressively from an axial orsubstantially axial direction to a radial or substantially radialdirection.
 4. The method as defined in claim 1, wherein circulating theexhaust flow through the exhaust passages of the recuperator furtherincludes reducing a swirl the exhaust flow through the exhaust passageshaving an arcuate profile in a plane perpendicular to a central axis ofthe recuperator.
 5. The method as defined in claim 1, further comprisingdelivering the exhaust flow from the exhaust passages to atmosphere. 6.The method as defined in claim 1, wherein the progressively increasingcross-sectional area of the exhaust passages is defined at least in acurved portion of the exhaust passages.
 7. The method as defined inclaim 1, wherein cooling the exhaust flow includes circulating theexhaust flow through the exhaust passages and circulating the airthrough the air passages in a mixed counter flow and double pass crossflow configuration.
 8. The method as defined in claim 1, whereincirculating the air discharged from the compressor section includescirculating the air through a plenum in fluid flow communication with adischarge of a compressor of the compressor section and from the firstplenum to the air passages.
 9. The method as defined in claim 1, whereincirculating the air to the combustor includes circulating the air fromthe air passages to a plenum containing the combustor.
 10. The method asdefined in claim 8, wherein the plenum is a first plenum, andcirculating the air to the combustor includes circulating the air fromthe air passages to a second plenum containing the combustor.